Autoimmune Lymphoproliferative Syndrome (ALPS) is a primary immunodeficiency of T cell dysregulation caused by defective Fas-mediated apoptosis. Many patients with ALPS develop a severe form of the illness with significant lymphadenopathy, splenomegaly, autoimmune disease, and increased risk of malignancy. Unfortunately, most therapies currently used to treat ALPS patients are non-specific, toxic, and ineffective. We recently demonstrated that targeting mTOR signaling with the mTORC1 inhibitor sirolimus is effective in preclinical models and in children with ALPS. While targeting mTORC1 was often effective, occasionally responses were less robust and with time relapses can occur. We have data that suggest Akt is abnormally activated in ALPS, specifically in the presumed effector cells of the disease double-negative T cells (DNTs). The abnormal activation of Akt may explain: (1) the profound response to mTORC1 inhibitors in most patients, because mTORC1 is a principal down-stream target of Akt; (2) the partial response in a subset of patients, because Akt activates additional pathways beyond mTORC1 that may drive disease; and (3) the development of resistance in a subset of patients, because continual exposure to mTORC1 inhibition can lead to feedback activation of Akt and related pathways. We hypothesize that ALPS cells have intrinsic abnormalities in Akt signaling, specifically abnormal constitutive activation of Akt in the DNT compartment. We will test this hypothesis using transgenic mouse models of ALPS and in lymphocytes from ALPS patients. We have developed novel in vitro and in vivo systems to support cells collected from children with ALPS. We propose two specific aims to validate our primary hypothesis. Aim 1: We will define the role of Akt in ALPS by performing a mechanistic analysis of the Akt pathway in ALPS cells, comparing signaling in DNTs with other lymphocytes. In addition, we hypothesize that the chronic defective Fas-mediated apoptosis found in ALPS leads to decreased distribution of Fas into lipid rafts which causes aberrant Akt activation in certain cells. We hypothesize that the development of abnormal activation of Akt in non-thymic DNTs leads to and drives the disease. We will study these hypotheses with our models. Aim 2: We will determine the efficacy of targeting Akt in ALPS. We will investigate two approaches to inhibit Akt: (1) direct inhibition, using Akt specific inhibitors, and (2) indirect inhibition by combined targeting of up-stream (PI3K or mTORC2) and down-stream (mTORC1, GSK3, or NfkB) effectors of Akt. We hypothesize both approaches will not only be effective, but be more effective than targeting mTORC1 alone. We have a track record of successfully moving discoveries made in the laboratory quickly into patients with ALPS. We anticipate these studies will allow us to revolutionize the treatment of ALPS, improving patient health and quality of life. PUBLIC HEALTH RELEVANCE: Autoimmune Lymphoproliferative Syndrome (ALPS) is a challenging childhood primary immunodeficiency disease, as current treatments are non-specific, toxic, and ineffective. We have data that strongly suggest disease develops in ALPS patients because of increased activation of a protein called Akt in abnormal ALPS cells. We propose to study Akt in ALPS cells and treat ALPS using innovative Akt-targeted therapies, leading to a better understanding of this disease and potentially even a cure for this often devastating childhood illness.